This project will characterize the mechanism of action of the antitumor protein, macromomycin. The biological activities of purified macromomycin (therapeutic effectiveness, inhibition of cell growth, DNA synthesis, and the strand scission of cellular DNA and cell free DNA) will be studied to see if they all originate with the single protein. Kinetic analysis of changes in the drug's biological activities as a function of protein denaturation will be used to help determine which drug effects are primary in regard to the drug's cytostatic activity. The mechanism of drug inhibition of DNA synthesis and breakdown of DNA will be examined and a relationship sought between the effect of the drug on DNA function and structure to its ability to inhibit cell growth. A second major aspect of this project will be a study of the interaction of macromomycin with the cell plasma membrane. The nature of macromomycin contact with the cell surface will be examined to see if there are specific drug binding sites. Trypsin rescue of drug-treated cells from the cytostatic effect of macromomycin will be explored to see if there are also changes in the drug effect on DNA during the resumption of cell growth. Macromomycin interaction with cell surface membranes will be examined to determine if there is a relationship between the drug-membrane interaction and the subsequent damage to the cellular DNA. Other DNA reactive antitumor drugs also thought to damage DNA and to have an interaction with the cell membranes (protein and glycopeptide DNA strand scission drugs and anthracycline DNA intercalating drugs) will be used in drug combination studies with macromomycin to see if there are common cell surface binding sites for these types of drugs.